Dynamic Driving Safety Systems

Transcription

1 Training Manual Dynamic Driving Safety Systems CT-L2003

2 No part of this hardcopy may be reproduced in any form without prior permission of Mazda Motor Europe GmbH. The illustrations, technical information, data and descriptive text in this issue, to the best of our knowledge, were correct at the time of going to print. No liability can be accepted for any inaccuracies or omissions in this publication, although every possible care has been taken to make it as complete and accurate as possible Mazda Motor Europe GmbH Training Services

3 Dynamic Driving Safety Systems Table of Contents Introduction Fundamentals Forces Acting on the Vehicle Yaw Moment Longitudinal Force Lateral Force Vertical Force Coefficient of Friction Wheel Slip Kamm s Circle Antilock Brake System Electronic Brakeforce Distribution Traction Control System Dynamic Stability Control Emergency Brake Assist Antilock Brake System Parts Location Hydraulic Unit / Control Module Wiring Diagram Layout Hydraulic Circuit Hydraulic Diagram Operation During Normal Braking During ABS Control Pressure Hold Mode Pressure Reduction Mode Pressure Increase Mode Servicing Bleeding Diagnostics Replacement Wheel Speed Sensor Passive Wheel Speed Sensor Diagnostics Checking the Air Gap Active Wheel Speed Sensor Diagnostics Brake Switch Diagnostics ABS Warning Light Diagnostics Curriculum Training

4 Table of Contents Dynamic Driving Safety Systems ABS on Vehicles with 4WD G-Sensor Diagnostics Replacement Electronic Brakeforce Distribution Brake System Warning Light Diagnostics Traction Control System TCS Control Module Wiring Diagram Hydraulic Circuit Hydraulic Diagram During TCS Control Pressure Increase Mode Pressure Hold Mode Pressure Reduction Mode Bleeding Diagnostics TCS Indicator Light Diagnostics TCS OFF Indicator Light Diagnostics TCS OFF Switch Diagnostics TCS on Vehicles with 4WD Curriculum Training

5 Dynamic Driving Safety Systems Table of Contents Dynamic Stability Control Parts Location Wiring Diagram Hydraulic Circuit Hydraulic Diagram Operation During DSC Control Pressure Increase Mode Pressure Hold Mode Pressure Reduction Mode Bleeding Diagnostics Combined Sensor Diagnostics Replacement Steering Angle Sensor Diagnostics Replacement Brake Fluid Pressure Sensor Diagnostics Replacement DSC Indicator Light Diagnostics DSC OFF Indicator Light Diagnostics DSC OFF Switch Diagnostics Emergency Brake Assist Electronic EBA Mechanical EBA Overview Operation Normal Braking Emergency Braking List of Abbreviations Curriculum Training

6 Table of Contents Dynamic Driving Safety Systems Notes: Curriculum Training

7 Dynamic Driving Safety Systems Introduction Introduction Recent decades have witnessed an ongoing series of advances in driving safety and comfort of automotive suspension. But ever-higher engine power and growing traffic volume have led to an increasing demand to improve the active driving safety of automobiles. However, a consistent stability in critical driving situations had to wait until advent of electronic control systems. The ever increasing use of electronics in vehicle systems has led to highly precise and miniaturized sensors that can exactly detect dynamic forces created during acceleration, deceleration, and cornering. These sensors and an appropriate electronic control system have been the crucial prerequisite for the development of dynamic driving safety systems that help the driver maintain vehicle control in critical driving situations. Although the dynamic driving safety systems offer a huge advantage for the passenger safety, it should be remembered that the extended driving safety does not extend the physical limitations valid for all vehicles. The following dynamic driving safety systems are used on current Mazda models and will be described in this training manual: Antilock Brake System (ABS) Electronic Brakeforce Distribution (EBD) Traction Control System (TCS) Dynamic Stability Control (DSC) Emergency Brake Assist (EBA) The skills needed to diagnose and repair dynamic driving system related concerns require comprehensive system knowledge, because any mistake can lead to malfunctions on the brake system and consequently affect the passenger s safety. This course is a theoretical and practical guide to gain general and Mazda specific knowledge about the various driving dynamics safety systems, i.e. their components, function and diagnosis. Any person involved in the diagnosis and repair of the dynamic driving safety system must have the knowledge to deliver a Fix it right first time repair. The Mazda Masters Development and Qualification path provides the following training course required for the service on the dynamic driving safety system. Dynamic Driving Safety Systems CT-L 2003 The ranking of this course within the Mazda Masters educational system is Level 2 Senior Technician. It is focused on technicians who have passed the Mazda Technician level already. Curriculum Training 00-1

8 Introduction Dynamic Driving Safety Systems The training manual Driving Dynamic Safety Systems is divided into the following main chapters: Introduction Fundamentals Antilock Brake System Electronic Brakeforce Distribution Traction Control System Dynamic Stability Control Emergency Brake Assist NOTE: The data, tables and procedures represented in this training manual serve only as examples. They are taken from the service literature and subjected to major or minor changes over the course of time. To prevent any misdiagnosis always refer to the current service literature while working on the driving dynamic safety system Curriculum Training

9 Dynamic Driving Safety Systems Fundamentals Fundamentals Various forces, that constantly change depending on the driving situation, determine the driving stability of a normal passenger vehicle. Whether or not these forces are properly transferred to the road completely depends on the four contact areas of the tyres; each one barely the size of a postcard! The key for this transfer is the right amount and type of friction between tyre and road surface. In the event the traction between tyre and road surface is lost, because the affecting forces have exceeded an appropriate limit, the vehicle handling becomes instable. The dynamic driving safety systems monitor specific parameters that indicate an impending traction loss of the wheels or vehicle skidding. In case of such situations the respective system counteracts this development by modulating either the brake pressure and / or the engine torque to maintain the vehicle stability. Curriculum Training 01-1

10 Fundamentals Dynamic Driving Safety Systems Forces Acting on the Vehicle A large number of forces act on a vehicle during driving. The forces most important for understanding the dynamic driving system are shown in the illustration below. 1 Yaw moment 4 Vertical force 2 Longitudinal drive force 5 Longitudinal brake force 3 Lateral force L2003_ Curriculum Training

11 Dynamic Driving Safety Systems Fundamentals Yaw Moment The yaw moment around the vehicle s vertical axis is caused by different longitudinal forces acting on the left and right side of the vehicle, or different lateral forces acting at the front and rear axles. Yaw moments are required to turn the vehicle when cornering. Undesired yaw moments can occur when a vehicle rotates too strongly around the yaw axis. Longitudinal Force During driving, accelerating, decelerating, and braking, the longitudinal force acts in the driving direction of the vehicle. Lateral Force The lateral force, that is applied to the vehicle by wind and cornering, acts sideways on the vehicle. Vertical Force The vertical force is the weight that is transmitted vertically by a tire. It depends on the vehicle s gross weight, the vehicle s centre of gravity, and other dynamic influences. Curriculum Training 01-3

12 Fundamentals Dynamic Driving Safety Systems Coefficient of Friction The frictional force is additionally affected by the coefficient of friction, which differs according to the materials and the surfaces rubbing against each other. The illustration shows that less force is necessary to push the larger weight across iced tarmac. It can be easily seen that the force required is much less than the vertical force due to the object s gross weight. The relationship between the frictional force and the vertical force is the coefficient of friction μ: Frictional force μ= Vertical force A Small weight on tarmac 2 Frictional force B Heavy weight on iced tarmac 3 Vertical force 1 Necessary force to push the object L2003_ Curriculum Training

13 Dynamic Driving Safety Systems Fundamentals The illustration shows the relationship between the tire downforce and the friction on a vehicle. 1 Linear velocity of the vehicle 3 Frictional force 2 Tire downforce L2003_01017 The table shows some sample values for the coefficient of friction between a tire and the road surface at various conditions. Vehicle speed 50 km/h 90 km/h 130 km/h Tire condition New Worn New Worn New Worn Dry road 0,85 1 0,8 0,95 0,75 0,9 Rain (depth of water approx. 0.2 mm 0,65 0,5 0,6 0,2 0,55 0,2 Heavy rain (depth of water approx. 1 mm) 0,55 0,4 0,3 0,1 0,2 0,1 Puddles (depth of water approx. 2 mm) 0,5 0,25 0, Icy road 0,3 < 0.1 < 0.1 < 0.1 < 0.1 < 0.1 L2003_T01001 Curriculum Training 01-5

14 Fundamentals Dynamic Driving Safety Systems Wheel slip The wheel speed is, depending on the driving conditions, more or less different to the actual vehicle speed (what is the theoretical wheel speed). The difference between the theoretical and the actual wheel speed is the wheel slip. The circumferential speed of a driven wheel is higher than the vehicle speed during accelerating, and the circumferential speed of a braked wheel is less than the vehicle speed. The relationship between the speed difference (between vehicle speed and wheel speed) and the vehicle speed is the wheel slip λ: λ = Vehicle speed - wheel speed Vehicle speed * 100 The wheel slip λ is calculated as a percentage. A fully locked wheel during driving, or a spinning wheel while the vehicle is stationary has a slip of 100 % while a wheel rotating with the vehicle speed has a slip of 0 %. The correct wheel slip is very important for the stability and driveability of a vehicle. Since the most force can be transmitted with a wheel slip of approximately 20 %, the ABS keeps the wheel slip between approximately % in order to achieve a short braking distance while maintaining high driving stability and steerability of the vehicle. 1 Circumferential wheel speed 2 Vehicle speed L2003_ Curriculum Training

15 Dynamic Driving Safety Systems Fundamentals The illustration below shows the influence of the wheel slip to the coefficient of friction between a tire and a dry normal road. X Wheel slip Y Coefficient of friction L2003_01015 Curriculum Training 01-7

16 Fundamentals Dynamic Driving Safety Systems Kamm s Circle A tire transmits both longitudinal and lateral forces to the road surface. Both forces form the resulting force that must be transmitted by the tire. A completely blocked wheel can no longer exert any cornering force. On the other hand, a vehicle that is subjected to additional braking when being pushed to the limit of adhesion during cornering will start to skid. The dependence on longitudinal and lateral force is shown in the so-called Kamm s circle. As long as the resulting force remains within the illustrated circle, driving stability of the vehicle is ensured. If the resulting force leaves the circle, the vehicle becomes unstable and skids. NOTE: The diameter of the Kamm s circle, (the maximum transmittable force) depends on the above mentioned values. 1 Lateral force 3 Longitudinal force 2 Resulting force L2003_ Curriculum Training

17 Dynamic Driving Safety Systems Fundamentals The illustration below shows the dependency between longitudinal and lateral force in a diagram. X Slip 2 Lateral force Y Transmittable force 3 Stable driving condition 1 Longitudinal force 4 Instable driving condition L2003_01018 Curriculum Training 01-9

18 Fundamentals Dynamic Driving Safety Systems Antilock Brake System Although all Mazdas are equipped with powerful and reliable brake systems that provide excellent braking power even at high speeds, a standard brake system cannot prevent a driver from over-reacting in an emergency situation and applying too much force to the brake pedal (especially under bad road / weather conditions or in case of an emergency braking). If the driver applies too much force to the brake pedal, the wheels will lock-up and the vehicle might skid, especially on irregular road surfaces. L2003_ Curriculum Training

19 Dynamic Driving Safety Systems Fundamentals Even if the vehicle does not skid, an accident may result, because it is not possible for the driver to steer around an obstacle with locked wheels. L2003_01009 The brake pressure regulation of the ABS prevents the wheels from locking-up. It applies the correct brake pressure to all brake callipers to maintain the vehicle s steerability while simultaneously achieving a short braking distance. L2003_01010 Curriculum Training 01-11

20 Fundamentals Dynamic Driving Safety Systems Electronic Brakeforce Distribution On former vehicles, only mechanical solutions were used for brakeforce distribution between the front axle and the rear axle. One of the disadvantages was that, to avoid early wheel lock-up under all circumstances (e.g. due to wet or slippery roads), the brake pressure applied to the rear wheels was never optimal. Now all Mazdas with ABS also have EBD, which allows the brakeforce distribution between the front and the rear axles to be adjusted based on actual conditions. Under most conditions the proportion of the brakeforce applied to the rear wheels is increased, resulting in optimal vehicle stability during all conditions. This results in: reduced braking distance, reduced thermal stress to the front brakes, and evenly worn front and rear brake pads. While a standard vehicle had a brakeforce distribution of approx. 80 % to the front wheels and 20 % to the rear wheels, the brakeforce distribution for vehicles with EBD changes up to approximately 60 % to 40 % (variable) Curriculum Training

21 Dynamic Driving Safety Systems Fundamentals The illustration shows the differences in applied brakeforce between a vehicle with fixed brakeforce distribution and with EBD. L2003_01011 X Brakeforce applied to the front wheels 3 Ideal brakeforce distribution on the unloaded vehicle Y Brakeforce applied to the rear wheels 4 Brakeforce distribution on the unloaded vehicle with EBD 1 Ideal brakeforce distribution on the fully loaded vehicle 5 Brakeforce distribution with proportioning valve (unloaded and fully loaded) 2 Brakeforce distribution on the fully loaded vehicle with EBD Curriculum Training 01-13

22 Fundamentals Dynamic Driving Safety Systems The first portion of the illustration (areas 1 and 2) shows the range of wheel slip where the EBD and ABS operate. The remaining part of the illustration shows the conditions of less than optimal brakeforce / steerability. X Wheel slip 2 ABS operation range Y Coefficient of dynamic friction 3 Instable driving condition 1 EBD operation range 4 Locking wheel L2003_ Curriculum Training

23 Dynamic Driving Safety Systems Fundamentals Traction Control System Critical driving situations can occur not only during braking, but also while driving, cornering, starting off, and accelerating (especially on wet or slippery roads). These situations can make it difficult for the driver to react correctly, and can cause the vehicle to become unstable. The TCS helps to solve these problems by avoiding / reducing wheel spin. This is achieved either by reducing the engine torque by sending a corresponding signal to the PCM (Powertrain Control Module) and / or by applying brakeforce to the spinning wheel(s). The TCS is incorporated to some ABS Hydraulic Unit/Control Module by minor changes to the basic system, but is also integrated to all DSC systems installed on Mazda vehicles. Depending on the vehicle, different strategies may be used for the operation of the TCS. The most common is that, when the control module recognizes that the wheel speed of the driven wheels exceeds the wheel speed of the other wheels by a specified value, a signal is sent to the PCM to reduce the engine torque. The PCM accordingly reduces the engine torque output by closing the throttle valve (only on vehicles with electronic throttle valve), adjusting the ignition timing, and / or by cutting fuel off. If the wheel spin still exceeds the limit or if the speed of one wheel exceeds the wheel speed of the other driven wheel by a specified value, brake force is applied by the hydraulic unit to the corresponding wheel(s). NOTE: TCS does not completely avoid wheel spin, it operates only above a specified limit of wheel spin. Curriculum Training 01-15

24 Fundamentals Dynamic Driving Safety Systems L2003_ RF wheel 8 Powertrain control module 2 RR wheel 9 Signal for torque reduction 3 LR wheel 10 ABS/TCS HU/CM 4 LF wheel 11 Applied brake fluid pressure 5 Transmitted torque 12 Brake calliper 6 Engine with transmission 13 Differential 7 Engine control Curriculum Training

25 Dynamic Driving Safety Systems Fundamentals Dynamic Stability Control Due to external circumstances, such as an obstacle on the road, wet or slippery roads, or driving at inappropriate vehicle speed, a vehicle can reach critical limits, where the driver cannot keep the vehicle under control anymore. The DSC improves vehicle handling and stability in these critical situations. A vehicle s driving direction can be controlled by either turning the steering wheel or by a yaw moment built up by applying brake force to one wheel. The driver uses the steering wheel, whereas the DSC uses the brake system to control the vehicles driving direction. The DSC constantly monitors the vehicle s movement, not only the speed, but also the yaw rate, the lateral acceleration, and the steering angle. The control module calculates the direction the driver wants to drive to by using the steering angle. This is compared to the actual vehicle speed, the vehicle s yaw rate, and lateral acceleration. If a critical situation is detected, the DSC accordingly applies controlled brakeforce and reduces the engine torque output as required (in the same way as for TCS operation), to ensure that the vehicle follows the desired direction. The DSC uses an advanced ABS HU/CM and additional sensors. Curriculum Training 01-17

26 Fundamentals Dynamic Driving Safety Systems The illustration shows the vehicle handling with and without DSC intervention in a critical situation. Obstacle suddenly appearing, vehicle without DSC L2003_01016 Obstacle suddenly appearing, vehicle with DSC L2003_ Curriculum Training

27 Dynamic Driving Safety Systems Fundamentals Emergency Brake Assist Although all Mazdas are equipped with powerful and reliable brake systems that provide excellent braking power even at high speeds, a standard brake system cannot prevent a driver from reacting incorrectly and applying less force to the brake pedal than required to achieve the shortest braking distance. Especially when the brake pedal starts vibrating due to ABS operation, many drivers either instinctively release the brake pedal, or do not increase the applied force further, which does not allow all the wheels to transmit the maximum possible brakeforce. The EBA automatically detects emergency braking situations by a combination of the speed and force with which the driver presses the brake pedal. Once such a situation is detected, the EBA automatically applies full brake pressure to both brake circuits, until either the driver fully releases the brake pedal and / or the vehicle comes to a stand still (depending on the vehicle). Of course the vehicle remains steerable during brake actuation, because the ABS ensures that no wheel locks up. The EBA is either incorporated into the ABS/DSC HU/CM and operates electronically, or it operates mechanically and is incorporated into the brake booster. The illustration shows typical differences during emergency braking with and without EBA. X Time 2 Experienced driver without EBA Y Brake fluid pressure 3 Average driver without EBA 1 Average driver with EBA L2003_01014 Curriculum Training 01-19

28 Fundamentals Dynamic Driving Safety Systems Notes: Curriculum Training

29 Dynamic Driving Safety Systems ABS Antilock Brake System Parts Location The picture is an example and shows the components of the Antilock Brake System (ABS) on a Mazda3. The ABS consists of the following components: Control module Hydraulic unit Wheel speed sensor Brake switch Brake system warning light ABS warning light L2003_ ABS warning light 6 ABS HU/CM 2 Brake system warning light 7 Front ABS pulse rotor 3 Rear ABS wheel-speed sensor 8 Front ABS wheel-speed sensor 4 Rear ABS pulse rotor 9 PCM 5 Brake switch Curriculum Training 02-1

30 ABS Dynamic Driving Safety Systems Hydraulic Unit / Control Module The ABS HU/CM (Hydraulic Unit / Control Module) is located in the engine compartment and is the core component of the ABS. As the name suggests, it controls the hydraulic operation of the ABS. It regulates the pressure in the brake lines to prevent the wheels from locking up during braking. This helps the vehicle remain steerable even during emergency braking. Most Mazda vehicles have a control module that is combined with the hydraulic unit. Depending on the vehicle it is possible to replace only a HU or a CM. On other vehicles, whenever there is a malfunction in one of the components, the entire HU/CM needs to be replaced as a complete unit. The last Mazdas built with a control module separated from the HU (i.e. the CM module is located elsewhere) were the 323 (BJ) with DSC and the Premacy (CP) with DSC. The ABS HU/CM is connected to all ABS related components and is programmed with vehicle-specific parameters. The CM decides whether or not it is necessary to assist the driver in using the brake system, and accordingly operates the brake system via the HU. The CM is connected to all electrical components of the ABS. It activates the valves and the pump motor inside the HU, the warning light in the IC (Instrument Cluster), and monitors the components and wiring for malfunction. It provides the power supply for the wheel speed sensors (only vehicles with active wheel speed sensors), and receives the wheel speed signals. Based on those signals it calculates the speed of each wheel individually and the vehicle speed. The difference calculated between the individual wheel speed and the vehicle speed indicates the slip of each wheel. The wheel speed sensors and the components inside the HU are hardwired to the CM. Other components can be either hardwired or connected via CAN. The HU is designed to regulate the pressure in the brake lines according to signals from the CM. In addition to maintaining the steerability, the regulation of the brake fluid pressure also helps decrease braking distance, wheel spin during acceleration (vehicles with TCS), and understeering/oversteering during cornering (vehicles with DSC). The components inside the HU are only operated when ABS operation is required. Then the CM accordingly actuates the pump motor and the valves. NOTE: Depending on the model, the ABS HU/CM performs a selftest at a vehicle speed of approximately 20 km/h after switching the ignition on. An operating pump during this selftest does not indicate a malfunction Curriculum Training

31 Dynamic Driving Safety Systems ABS The HU consists of the hydraulic pump and of 6 12 solenoid controlled hydraulic valves. One inlet and one outlet valve for each wheel (for B-Series only one inlet and one outlet valve for the rear axle), two traction control valves for vehicles with TCS and two additional stability control valves for vehicles with DSC. The HU cannot be disassembled. Most HUs feature a flow control valve downstream of each inlet valve. The flow control valve has been integrated to reduce the brake fluid flow noise by narrowing a passage, and is actuated hydraulically in case of a high-pressure difference upstream and downstream of the inlet valve. NOTE: Always keep in mind, that the Dynamic Driving Safety Systems cannot override the law s of physics. 1 Control module 4 ABS pump motor 2 Hydraulic unit 5 Lock lever for connector 3 Brake pipe 6 ABS connector / wiring loom L2003_02002 Curriculum Training 02-3

32 ABS Dynamic Driving Safety Systems Wiring Diagram Mazda3 L2003_ ABS fuse 1 11 Battery 2 ABS fuse 2 12 ABS pump motor 3 ABS fuse ignition ON 13 CAN H 4 Solenoid valves 14 CAN L 5 Brake system warning light 15 ABS wheel-speed sensor LR 6 ABS warning light 16 ABS wheel-speed sensor RR 7 CAN driver 17 ABS wheel-speed sensor LF 8 IC 18 ABS wheel-speed sensor RF 9 PCM 19 ABS HU/CM 10 DLC Curriculum Training

33 Dynamic Driving Safety Systems ABS Layout Current Mazda models use ABS with 4 wheel speed sensors and a three or four channel layout: A three channel layout provides ABS control for each front wheel individually and for the rear wheels in common according to the select low principle. The B-Series is the only Mazda vehicle still featuring this layout. Select low principle means an ABS control strategy adjusting brake pressure for both rear wheels determined by the wheel that tends to lock first. Because, the largest influence on a vehicle s driving stability is the ability of the rear axle to continue to travel in the desired direction. A four channel layout allows individual brake pressure control for each wheel. This is required when either the brake system has a diagonal split layout, as all Mazda models with front wheel drive have, or when a rear wheel driven vehicle has TCS. During ABS operation the rear axle is also controlled corresponding to the select low principle. A four channel layout is mandatory for DSC. Hydraulic Circuit The hydraulic circuit that is explained on the following pages, is a four channel ABS. A three channel ABS operates similar, except for the fact, that it features only 6 solenoid valves. The HU for a 4 channel ABS is equipped with 8 solenoid valves that can be activated for the ABS operation. Four of those valves are the inlet valves, they are used to separate each single brake calliper from the brake master cylinder and avoid further pressure increase if the corresponding wheel is about to lock-up. These valves are always open when not actuated. The other four valves are the outlet valves. They are necessary to be able to release pressure from each single brake calliper to reduce the applied brake force on each wheel individually, if a wheel is still about to lock-up after the inlet valve has been closed. These valves are always closed when not actuated. Curriculum Training 02-5

34 ABS Dynamic Driving Safety Systems Hydraulic Diagram Mazda3 L2003_ Master cylinder 7 Inlet solenoid valve 2 ABS HU/CM 8 Outlet solenoid valve 3 Damper chamber 9 Brake calliper LF 4 Pump motor 10 Brake calliper RR 5 Pump 11 Brake calliper LR 6 Reservoir 12 Brake calliper RF Operation For easier understanding, only the operation of the left front brake circuit is explained. The other circuits act similarly Curriculum Training

35 Dynamic Driving Safety Systems ABS During Normal Braking During normal braking, the solenoid valves are not energized. When the brake pedal is pressed, brake fluid pressure is built up by the master cylinder and passes through the inlet solenoid valves and then to the brake callipers. The brake fluid pressure is fully controlled by the driver. When the brake pedal is released, the pressure decreases the opposite way it was built up. Inlet solenoid valve Outlet solenoid valve Pump motor OFF (open) OFF (closed) OFF (stopped) L2003_T02001 L2003_ Master cylinder 6 Reservoir 2 ABS HU/CM 7 Pump motor 3 Outlet solenoid valve 8 Pump 4 Brake calliper 9 Damper chamber 5 Inlet solenoid valve Curriculum Training 02-7

36 ABS Dynamic Driving Safety Systems During ABS Control When wheel lock-up is about to occur, the system starts with the ABS control operation. ABS can operate three ways: Pressure hold mode Pressure reduction mode Pressure increase mode (which is the same as the Normal Braking already explained on the previous page) Pressure Hold Mode When the CM detects wheel slip increasing above a specified value, it holds constant the brake force applied to that wheel to avoid lock-up. Therefore, it energises the corresponding inlet solenoid valve, closing the hydraulic circuit between the brake calliper and the brake master cylinder. Thus, the brake fluid pressure inside the related brake calliper cannot increase further. Even if the driver presses the brake pedal further and the brake fluid pressure in the master cylinder increases, the brake pressure will not increase on a wheel that is currently in pressure hold mode. Inlet solenoid valve Outlet solenoid valve Pump motor ON (closed) OFF (closed) OFF (stopped) L2003_T Curriculum Training

37 Dynamic Driving Safety Systems ABS L2003_ Master cylinder 6 Reservoir 2 ABS HU/CM 7 Pump motor 3 Outlet solenoid valve 8 Pump 4 Brake calliper 9 Damper chamber 5 Inlet solenoid valve Curriculum Training 02-9

38 ABS Dynamic Driving Safety Systems Pressure Reduction Mode When the CM detects that wheel slip is still increasing and reaches a specified value, it reduces the brake force applied to that wheel. The inlet solenoid valve remains actuated and additionally the appropriate outlet solenoid valve and the pump motor are energised. Thus the brake fluid pressure in the brake calliper decreases and the released brake fluid is pumped from the reservoir towards the brake master cylinder. Inlet solenoid valve Outlet solenoid valve Pump motor ON (closed) ON (open) ON (operating) L2003_T02003 L2003_ Master cylinder 6 Reservoir 2 ABS HU/CM 7 Pump motor 3 Outlet solenoid valve 8 Pump 4 Brake calliper 9 Damper chamber 5 Inlet solenoid valve Curriculum Training

39 Dynamic Driving Safety Systems ABS Pressure Increase Mode When the CM detects that the wheel slip decreases below a specified value, it increases the brake force to that wheel, in order to keep the wheel slip in the specified range. It deactivates the inlet and outlet solenoid valve and the pump. Thus, the pressure increase is performed in the same way as during normal braking, the brake pressure is increased by the driver s foot, still pressing the brake pedal. Inlet solenoid valve Outlet solenoid valve Pump motor OFF (open) OFF (closed) OFF (stopped) L2003_T02004 These three modes are repeated as required until either: the brake pedal is released, the speed of the vehicle is below the specified value for ABS operation (approx km/h, depending on the vehicle) or the wheel slip does not exceed the specified value anymore. L2003_02008 X Time 2 Calculated vehicle speed Y1 Speed 3 Pressure increase Y2 Solenoid valve control 4 Pressure hold Y3 Brake fluid pressure 5 Pressure reduction 1 Wheel speed Curriculum Training 02-11

40 ABS Dynamic Driving Safety Systems Servicing The ABS HU contains delicate mechanical parts. If foreign materials get into the component the ABS may fail to operate. Also, it will likely become extremely difficult to find the location of the malfunction in the event that the brakes operate but the ABS does not. Make sure foreign materials do not get inside when servicing the ABS (e.g. brake fluid replacement, pipe removal). To avoid trouble coming from the hydraulic system of the ABS and the brake it is best to protect the whole system with a regular exchange of brake fluid and flushing of the hydraulic ABS unit. NOTE: To avoid that the HU runs dry and air enters the HU, always install apropriate closing covers when removing hydraulic lines. Bleeding NOTE: In most cases it is not necessary to bleed the HU with the aid of the M-MDS during exchange of the brake fluid. Always follow the procedure of the corresponding W/M (Workshop Manual). If the ABS HU needs to be flushed or bled, it is necessary to switch on the pump and the outlet valves. NOTE: Always perform the manual bleeding procedure before performing any bleeding procedure with the aid of the M-MDS Connect the brake-bleeding device with the brake fluid reservoir ensuring that fresh brake fluid will get to the HU. For Mazda2 and Tribute the M-MDS provides the ABS Service Bleed function. Connect the M-MDS with DLC2 and select 16PINDLC Toolbox Chassis Braking ABS Service Bleed and follow the screen instructions Curriculum Training

41 Dynamic Driving Safety Systems ABS For models the M-MDS does not provide a service bleed function, ABS valves and the ABS pump can be activated via the Simulation Test Mode available in the DataLlogger menu. Connect the M-MDS and select Toolbox Datalogger Modules ABS Then select PIDs as displayed below. To start the activation of the valve and the pump in the HU: Select and activate ABS_POWER Select and activate the outlet solenoid valve of the corresponding brake calliper a bleeding bottle is connected with (here it is the left front side) LF_OUTLET and PMP_MOTOR NOTE: To prevent the ABS unit from overload, the solenoid valves and pump motor must not be activated permanently when bleeding. Depending on the model, the pump motor and the solenoid valves are either automtically deactivated 10 seconds after beeing activated with the aid of the M-MDS or they must be deactivated manually. L2003_02052 Repeat the procedure for each outlet valve. Curriculum Training 02-13

42 ABS Dynamic Driving Safety Systems Diagnostics The HU/CM can be checked by: Reading out DTCs Checking voltage signals Monitoring / Activating the corresponding PIDs (see below) NOTE: The ABS warning light might stay illuminated after deleting DTCs, until the unit performed a self test. Therefore it is necessary to perform a test drive after deleting DTCs. PID Definition Unit/Condition BOO_ABS Brake switch ON/OFF CCNTABS Number of detected DTCs - LR_OUTLET# LR ABS pressure outlet solenoid valve ON/OFF LR_INLET# LR ABS pressure inlet solenoid valve ON/OFF LR_WSPD LR ABS wheel-speed sensor input km/h, mph RR_INLET# RR ABS pressure inlet solenoid valve ON/OFF RR_OUTLET# RR ABS pressure outlet solenoid valve ON/OFF RR_WSPD RR ABS wheel-speed senosr input km/h, mph LF_INLET# LF ABS pressure inlet solenoid valve ON/OFF LF_OUTLET# LF ABS pressure outlet solenoid valve ON/OFF LF_WSPD LF ABS wheel-speed sensor input km/h, mph RF_INLET# RF ABS pressure inlet solenoid valve ON/OFF RF_OUTLET# RF ABS pressure outlet solenoid valve ON/OFF RF_WSPD RF ABS wheel-speed sensor input km/h, mph PMP_MOTOR# ABS motor ON/OFF L2003_T02006 NOTE: Depending on the model, the availability of the PIDs varies. In addition, different PID names may be used for identical parameters (see W/M). Replacement A new HU is usually delivered pre filled. Nevertheless, the brake system must be bled according to the W/M. A new CM must be configured (except for Mazda2 (DY) and B-Series (UN)) with the aid of the M-MDS, via the option Programmable Module Installation (refer to W/M). If a new DSC HU/CM has been installed, additional initialisation procedures of the sensors must be performed (refer to W/M) Curriculum Training

43 Dynamic Driving Safety Systems ABS Wheel Speed Sensor Depending on the vehicle, the ABS uses passive or active wheel speed sensors. Each wheel sensor sends a pulsed speed signal to the ABS control module. Based on those signals, the control module calculates the speed of each wheel and the vehicle speed. When a wheel speed difference occurs, while comparing the vehicle speed with each individual wheel speed, this is used as an indication of changing grip on an individual wheel. Based on this information, the ABS control module calculates the slip of each wheel during braking. With the aid of the ABS operation the ABS control module keeps the slip of the wheels in the range of % to ensure good steerability and high brake forces. Mazda3 L2003_ Wheel speed sensor 3 Wheel bearing 2 Steering knuckle 4 Pulse rotor Curriculum Training 02-15

44 ABS Dynamic Driving Safety Systems Passive Wheel Speed Sensor The passive wheel speed sensors are an inductive-type, i.e. the sensors produce an analog voltage signal via induction due to a changing magnetic field, caused by the turning wheel. Passive wheel speed sensors are installed on B-Series (UN), Premacy (CP), MX-5 (NB), Mazda6 (GG/GY), MPV (LW), and RX-8 (SE). The voltage output increases with increased wheel speed. With very low wheel speed (below approx. 6 km/h), the voltage output is too low to deliver a proper wheel speed signal to the CM. The CM uses the number of pulses per second to calculate the wheel speed. The vehicle speed is calculated by the CM, based on the wheel speed of all wheels. NOTE: Strong vibrations can demagnetise permanent magnets. Hammer blows in the vicinity of the wheel sensor (e.g. when repalcing a wheel bearing) could permanently damage the sensor, if it is not previously removed. 1 Wheel speed sensor 5 Pulse rotor 2 Permanent magnet 6 Air gap 3 Coil 7 Connection to ABS CM 4 Iron core L2003_ Curriculum Training

45 Dynamic Driving Safety Systems ABS L2003_ Wheel speed sensor 2 ABS HU/CM Diagnostics The inductive wheel speed sensor can be checked by: Reading out DTCs Checking the voltage signal Measuring its resistance Checking the air gap Monitoring the corresponding PIDs (see below) PID Definition Unit/Condition LF_WSPD LF ABS wheel-speed sensor input km/h, mph LR_WSPD LR ABS wheel-speed sensor input km/h, mph RF_WSPD RF ABS wheel-speed sensor input km/h, mph RR_WSPD RR ABS wheel-speed sensor input km/h, mph L2003_T02005 Curriculum Training 02-17

46 ABS Dynamic Driving Safety Systems Checking the Air Gap If the wheel speed signal is faulty, or when replacing a wheel speed sensor (active or passive), make sure to adjust the gap between the sensor and the rotor according to the W/M. If the gap is too large, this can cause inaccurate wheel speed signals. If the gap is too small, the rotor and the sensor could be damaged. NOTE: An air gap exceeding the specifications could be caused by excessive wheelbearing clearance. Keep the rotor and the sensor clean from metal debris and other dirt to ensure a proper signal is generated. 1 Wheel speed sensor 3 Pulse rotor 2 Gap L2003_ Curriculum Training

47 Dynamic Driving Safety Systems ABS Active Wheel Speed Sensor The active wheel speed sensors are either hall element type or giant magneto resistor type, i.e. the sensors need a power supply (provided by the CM) and output a rectangular signal with the aid of an integrated circuit. The height of the signal is not affected by the wheel speed. This means the active wheel speed sensor can transmit a proper wheel speed signal even at very low speeds (approx. 0.1 km/h). The CM uses the number of pulses per second to calculate the wheel speed. The vehicle speed is calculated by the CM based on the wheel speed of all wheels. NOTE: An active wheel speed sensor must not be inspected using an ohmmeter. NOTE: The difference between the High and Low signal can be as low as 0.2 Volt. NOTE: Strong vibrations can demagentise permanent magnets. Hammer blows in the vicinity of the magnetic layer on a wheel bearing (e.g. when replacing the bearing) could permanently damage the magnetic layer, causing a faulty wheel speed signal. A Detection principle 3 Magnetic rubber (magnetic encoder) B Output waveform 4 Semiconductor element 1 ABS wheel-speed sensor 5 Sensor output signal 2 Active drive circuit 6 Semiconductor element signal L2003_02011 Curriculum Training 02-19

48 ABS Dynamic Driving Safety Systems L2003_ Wheel speed sensor 2 ABS HU/CM Diagnostics The active wheel speed sensor can be checked by: Reading out DTCs Checking the voltage signal Checking the air gap Monitoring the corresponding PIDs (see below) PID Definition Unit/Condition LF_WSPD LF ABS wheel-speed sensor input km/h, mph LR_WSPD LR ABS wheel-speed sensor input km/h, mph RF_WSPD RF ABS wheel-speed sensor input km/h, mph RR_WSPD RR ABS wheel-speed sensor input km/h, mph L2003_T Curriculum Training

49 Dynamic Driving Safety Systems ABS Brake Switch The brake switch, which is actuated by the brake pedal, informs the ABS control module when the brake pedal is pressed. This signal is necessary to recognize that the driver wants to slow down the vehicle using the brake. The ABS will not start operating until a corresponding signal from the brake switch is received. The brake switch is a standard On/Off switch that is either hardwired to the ABS control module or its information is forwarded via CAN (e.g. on Mazda6 F/L where it is hardwired to the PCM and forwarded from there via HS-CAN to the ABS control module). NOTE: On some vehicles, if the brake switch has been removed it must be discarded, and a new one must be installed (refer to the W/M). 1 Brake pedal 3 Brake switch 2 Brake switch connector L2003_02013 Curriculum Training 02-21

50 ABS Dynamic Driving Safety Systems Diagnostics The brake switch can be checked by: Reading out DTCs Checking the voltage signal Measuring its resistance Monitoring the corresponding PID (see below) PID Definition Unit/Condition BOO_ABS Brake pedal switch ON/OFF L2003_T02028 ABS Warning Light The yellow ABS warning light is located in the IC. It illuminates after ignition on for a few seconds to inform the driver that the warning light has no malfunction. If it stays on or illuminates during driving, a malfunction has been detected. As long as the warning light is illuminated the ABS control is switched off, but the standard brake system is fully operational, if there is no other warning light illuminated. All current Mazda vehicles feature a DTC memory function, which stores the malfunction in the ABS control module. If a temporary malfunction has been detected that does not exist any more, the failure will be stored and the warning light will go off after switching the ignition off and on. L2003_ IC 2 ABS warning light Curriculum Training

51 Dynamic Driving Safety Systems ABS The ABS warning light is either hardwired to the ABS control module or switched from a microcomputer in the IC. In the second case the IC receives an ABS warning light ON request via CAN if the ABS CM detects a malfunction. If there is an open circuit between the ABS CM and the IC, the ABS warning light will be illuminated by the microcomputer or a transistor inside the IC. On earlier models a shortcircuit bridge was installed to the connector of the ABS CM to ensure that the warning light is illuminated if the connector is disconnected. CAN controlled 1 Brake system warning light 5 CAN driver 2 ABS warning light 6 CAN H 3 IC 7 CAN L 4 ABS HU/CM L2003_02015 Curriculum Training 02-23

52 ABS Dynamic Driving Safety Systems L2003_02047 Hard wired transistor controlled 1 ABS warning light 3 ABS CM 2 IC Diagnostics The ABS warning light can be checked by: Visually inspecting the warning light after switching the ignition on Checking voltage signals Using the input/output check mode for the IC Monitoring the corresponding PID (see below) PID Definition Unit/Condition ABS_LMP ABS warning light ON/OFF L2003_T Curriculum Training

53 Dynamic Driving Safety Systems ABS ABS on Vehicles with 4WD The ABS on vehicles with 4WD (4 Wheel Drive) is essentially the same as on other vehicles, except for the following features: A G-sensor (Gravity) has been installed on vehicles with 4WD. On the Mazda6, 4WD operation is disabled during ABS operation. To do so, the ABS HU/CM transmits a signal via CAN to the 4WD CM, and the 4WD CM correspondingly disables the electronically controlled clutch. G-Sensor On the B-Series the G-sensor is mounted under the passenger s seat, and on Mazda6 it is incorporated in the combined sensor, while on Tribute it is integrated in the ABS HU/CM. The G-sensor features a longitudinal accelerometer and is connected to the ABS HU/CM. It sends an acceleration/deceleration signal to the CM. The signal from the G-sensor is necessary as a vehicle speed correction factor. Because, on 4WD vehicles, under some circumstances, the movement of the vehicle cannot be measured as precisely as necessary when using the wheel speed sensors only. L2003_ Front of vehicle 4 Acceleration 2 G-Sensor 5 Neutral-G 3 Output voltage characteristics 6 Deceleration Curriculum Training 02-25

54 ABS Dynamic Driving Safety Systems L2003_ G-sensor 2 ABS HU/CM Diagnostics The G-sensor and 4WD related components can be checked by: Reading out DTCs Checking the voltage signal Monitoring the corresponding PIDs (see below) PID Definition Unit/Condition ACCLMTR Longitudinal acceleration in G G AWD_MSG Communication with 4WD CM (only on Mazda6) Present / Not Present L2003_T02012 Replacement If the G-sensor on a Mazda6 needs to be replaced, the new sensor must be initialised using the M-MDS (refer to W/M) Curriculum Training

55 Dynamic Driving Safety Systems EBD Electronic Brakeforce Distribution All current Mazdas with ABS have EBD (Electronic Brakeforce Distribution) which eliminates the need for a proportioning valve. The B-Series is the only current Mazda that still uses a proportioning valve (load sensing type) even though it is also equipped with EBD. The EBD is a function, which is programmed in the ABS CM and needs only minor modifications to the system. It allows the split in brake force to be adjusted much more accurately according to the current driving conditions. The EBD detects the difference in wheel slip between the front and rear wheels with the aid of the wheel speed sensors. If wheel slip of the rear wheels compared to the front wheels exceeds a specified limit, it reduces the brake fluid pressure applied to the rear wheels with the aid of the hydraulic valves in the ABS HU/CM. Handling response is continuously monitored and a larger proportion of the overall braking force can be applied to the rear brakes when conditions allow. This results in shorter brake distances and reduced wear due to less thermal stress on the front brakes. EBD operation stops when ABS operation starts. The graph shows when EBD operation begins, and when the CM changes to ABS operation mode. Furthermore you will notice that the operation by the CM is always done in advance, and that there is a difference in time between actuating the valves and the resulting change in pressure/speed. This is because the electronic control is much faster than hydraulics, and there is also an additional delay due to the momentum of the vehicle and wheels. Curriculum Training 02-27

56 EBD Dynamic Driving Safety Systems L2003_02017 X Time 5 EBD initial control value Y1 Speed 6 Pressure reduction Y2 Rear solenoid valve control 7 Pressure hold Y3 Brake fluid pressure 8 Pressure increase 1 Vehicle speed 9 Front brake fluid pressure 2 Rear wheel speed 10 Rear brake fluid pressure 3 Front wheel speed 11 ABS control range 4 ABS initial control value 12 EBD control range Curriculum Training

57 Dynamic Driving Safety Systems EBD Brake System Warning Light The EBD system uses the red brake system warning light to indicate a malfunction. The brake system warning light also indicates malfunctions concerning brake fluid level or parking brake operation, but whenever the light illuminates the EBD operation is disabled. NOTE: If a malfunction occurs and the EBD is disabled, the red brake system warning light will illuminate. If this happens the driver should stop immediately and check the brake fluid level and the brake pressure. If the brake fluid level and the brake pressure are okay, and the parking brake is released, the vehicle should be driven slowly, or towed by a professional towing service (refer to apropriate owners manual), to the workshop. Because, if the EBD system fails, the rear wheels can lock-up easily due to full brake pressure applied to the rear wheels. If this happens, the vehicle is difficult to steer and tends to skid during braking. 1 IC 2 Brake system warning light (red) L2003_02018 Curriculum Training 02-29

58 EBD Dynamic Driving Safety Systems Diagnostics Because the EBD is incorporated in the ABS HU/CM, there is no special procedure available for diagnosis of the EBD. The system is inspected together with the ABS HU/CM and the related components. The brake system warning light can be inspected: Visually, after switching the ignition on With the aid of the input/output check mode for the IC Monitoring the corresponding PID (see below) PID Definition Unit/Condition BRAKE_LMP Brake system warning light ON/OFF L2003_T Curriculum Training

59 Dynamic Driving Safety Systems TCS Traction Control System The TCS (Traction Control System) is installed on most Mazdas with ABS to ensure good traction for the driven wheels. Some earlier systems used only engine torque reduction through fuel cut-off and ignition timing control for TCS operation, others used only brake control. This course emphasizes systems installed on most current Mazda vehicles. It reduces engine torque and/or applies brake pressure to the spinning wheel, as needed. The system is incorporated into the ABS HU/CM. The TCS features the following changes in components over an ABS: Two traction solenoid valves are added to the HU/CM. A TCS OFF switch is added to the dashboard. A TCS OFF indicator light and a TCS indicator light are included in the IC. The CM can send a torque reduction signal to the PCM when required. Curriculum Training 02-31